The growth in the use of portable electronic devices such as mobile communication devices, cellular telephones and the like has driven the design of such devices to become smaller and more convenient. Consumers have become accustomed to the convenience and portability of such electronic devices, particularly, cellular telephones and other convergence devices, such as audio and audio-video devices with communication capabilities and have demanded that those devices become even more convenient and even more portable. The constant thrust in the portable device design is thus to make the device as small as possible.
Furthermore there is also an increasing demand for such devices to operate in a hands-free mode where the device is operational without requiring it to be held to the user's ear. For example an audio playback device which can be used without headphones or separate loudspeaker components. Such devices typically include an internal antenna and speaker component. The antenna component enables communication to other devices. For example such communication can be a “cellular” communication system or “wireless broadband” communication system, specific examples may be a WiFi connection, or a UMTS (universal mobile telecommunication system) connection. Such connections enable the device to communicate with other devices, for example to download further audio and video or hold a voice communication with a further device.
The mechanical design and operational consideration for the antenna and speaker must be taken into account to ensure the proper operation of each to obtain the desired results. The antenna includes an RF (Radio Frequency) emitter (which can equally be considered to be a receiver) that is generally held or placed in a spaced separation with respect to a ground plate mounted in the chassis of the device. The RF emitter electrically connects to the operational electronic circuitry of the mobile device and the spaced separation between the RF emitter and the ground plate area defines the mechanical outline of the antenna chamber volume. Furthermore the speaker component is in some designs located separate and away from the RF emitter to prevent interference with the emitter.
It is also a current requirement that the speaker component provides a sufficiently high air displacement and pressure to provide audio sounds loud enough to implement a hands-free operation. Typically this can be generated by having the speaker component mounted in an enclosure of some sort defining a chamber which enhances bass tone production. The physical size or volume of the chamber influences the audio quality as a larger volume generally results in better audio quality. A drawback with such traditional speaker components in meeting these audio quality requirements is their large physical size. One attempt to reduce the physical dimensions used by the antenna and chamber is the combined antenna speaker chamber configuration. This for example is shown in FIG. 2 whereby the antenna speaker chamber 60 comprises a planar antenna 70 and speaker 80 which share a common cavity or chamber 90 with a portion 92 of the chamber 90 located in the chamber 90 in the area beneath the antenna 70. The construction of the combined antenna speaker chamber thus combines the separate antenna and speaker chambers in an attempt to meet both the acoustic requirements and the radio frequency requirements of the mobile device. The volume of the chamber 90 is thus given by the width Wc multiplied by the height Hc multiplied by the length Lc where the length would be less than the individual lengths for the speaker chamber and the antenna.
In order to attempt to reduce the volume of the acoustic or speaker chamber in order to further reduce the size of such devices, it is known to use acoustically absorptive materials which increase the effective volume, reduce resonances and thus result in extended bandwidth improved efficiency and reduced coloration of the chamber. The use of absorptive materials in manufacturing produces a substantial increase in cost and as such is typically only justifiable where the effective volume is substantially increased. Materials such as plastic foams, synthetic or natural fibres do not produce sufficient efficiencies to cost of use ratio to warrant their manufacture. Materials with large surface activity such as zeolite derived products which can provide somewhere between 1.5 to 2.2 times the increase in an effective acoustic volume are furthermore difficult to handle in a manufacturing and as such are not suitable for mass production at sufficient economies. Activated carbon which is available in sheet form and thus suited for manufacturing although promising in producing similar volumetric efficiencies has a different problem in that the material is electrically conductive. This electrical conductivity causes RF losses due to conductive effects whereby the RF signal being transmitted or received generates currents within the sheet carbon reducing the electric field strength.
The use of carbon electrically conductive material thus while producing sufficient efficiencies in effective volume and being suitable for manufacturing causes significant losses in both transmission and reception when placed near the radio antenna.